The present invention relates to rotating biological contactor-type sewage treatment equipment.
A conventional example of rotating biological contactor-type sewage treatment equipment is disclosed in Japanese Patent Laid-open Publication No. H6-99184. This sewage treatment equipment includes a plurality of spaced rotating discs which are mounted on a rotating shaft. Each of the rotating discs is allowed to rotate, with a part of the disc being submerged in sewage in the treatment tank. In this equipment, sewage is treated through contact between the sewage and aerobic bacteria adhered to the rotating discs.
Such sewage treatment equipment is required to treat sewage efficiently, reduce the initial investment, cut the cost for maintaining its operation, simplify the operation management, and more. From these viewpoints, the above conventional technology has satisfied these requirements to a certain degree. Recently, however, there are additional demands for rotating biological contactor-type sewage treatment equipment which can achieve a further excellent sewage treatment performance and a greater cost reduction.
The present invention is made in the light of such circumstances, and intends to provide rotating biological contactor-type sewage treatment equipment which realizes a further excellent sewage treatment performance and a greater cost reduction.
In order to achieve the above object, the biological contactor-type sewage treatment equipment of the present invention comprises a treatment tank for storing sewage to be treated, a rotation shaft which extends across opposed side walls of the treatment tank, a plurality of rotating discs mounted at a predetermined interval on the rotation shaft in such a manner that each rotating disc is partly submerged in the sewage stored in the treatment tank, and a driving means for supplying a driving force to the rotation shaft in order to rotate the rotating discs, the sewage treatment equipment treating sewage by rotating the rotating discs on which aerobic bacteria are attached, thereby allowing the aerobic bacteria to contact the sewage and aerobically decompose pollutants in the sewage. This sewage treatment equipment is arranged such that each of the rotating discs is composed of n portions of sector-shaped segments, wherein n is an integer not less than 1, each of the sector-shaped segments being composed of two equally divided sector-shaped pieces and each of the sector-shaped pieces having thin elements which form meshes; that the meshes have the same size and shape except in the neighborhood of a periphery surrounding the each sector-shaped piece, and an arrangement of the meshes is regularly aligned in the same direction relative to one side of the each sector-shaped piece; that projections project from predetermined locations on the thin elements and extend perpendicularly relative to each surface of each rotating disc; and that, in an installation state where adjacent rotating discs are displaced from each other by 360xc2x0/2n in a direction of rotation, projections which locate on one of the adjacent rotating discs are oriented to openings in the meshes formed by the thin elements of another rotating disc.
The angle given by the general formula 360xc2x0/2n is one half the central angle of the sector-shaped segment, provided that one rotating disc is divided into n segments. In other words, regardless of the size and number of the sector-shaped segments, the rotating discs are displaced from each other by one half the central angle of one sector-shaped segment (the central angle of the sector-shaped piece).
The rotating discs applied to this arrangement are provided with square grid-like meshes as shown in FIG. 4, circular meshes 130 as shown in FIG. 13(a), parallelogramatic meshes 140 or rhombic meshes as shown in FIG. 13(b), etc. In the rotating discs shown in FIG. 4 and FIG. 13(b), the projections preferably locate at intersections 19c and intersections 141 of the thin elements, respectively. In the rotating disc shown in FIG. 13(a), projections are preferably provided at midpoints 131 of line segments connecting the centers of the circles.
Regarding the above arrangement, it is preferable that each of the sector-shaped pieces has thin elements which cross each other to form meshes; that the meshes have the same size and shape except in the neighborhood of a periphery surrounding the each sector-shaped piece, and an arrangement of the meshes is regularly aligned in the same direction relative to one side of the each sector-shaped piece; and that projections project from intersections of the thin elements and extend perpendicularly relative to each surface of each rotating disc.
The rotating discs which adopt this arrangement include, for example, those shown in FIG. 4 and FIG. 13(b).
Further in the above arrangement, it is preferable that the thin elements in each of the sector-shaped pieces form square grid-like meshes of the same size, except in the neighborhood of a periphery surrounding the each sector-shaped piece; and that the thin elements extend vertically and horizontally relative to one side of the each sector-shaped piece, with crossing each other.
The rotating discs which adopt this arrangement include, for example, the one shown in FIG. 4.
Preferably, between the two sector-shaped pieces which constitute the sector-shaped segment, the thin elements which extend vertically or horizontally relative to a side of one of the sector-shaped pieces are located at different positions, as compared with the thin elements which extend vertically or horizontally relative to a corresponding side of the other sector-shaped piece. Owing to this arrangement, in an installation state where adjacent rotating discs are displaced from each other by 360xc2x0/2n in a direction of rotation, projections which locate on one of the adjacent rotating discs are oriented to openings in the meshes formed by the thin elements of another rotating disc.
Additionally, in any of the above arrangements, each of the sector-shaped pieces preferably includes an insertion hole for passing a fixing rod which connects the plurality of rotating discs mounted at a predetermined interval, the insertion hole locating along a line which divides the each sector-shaped piece into two equal sector-shaped portions. This arrangement enables mutual connection of the rotating discs. Besides, with the rotating discs being fixed at the respective positions, the projections are positioned to orient to the openings in the meshes formed by the thin elements.
In the rotating biological contactor-type sewage treatment equipment of the present invention which adopts any of these arrangements, adjacent rotating discs which are spaced by a predetermined interval are displaced from each other by 360xc2x0/2n in a direction of rotation. Hence, with respect to the adjacent rotating discs 1, 1, projections provided along the meshes of a first rotating disc are oriented to openings surrounded by the thin elements which form the meshes in a second rotating disc, and projections provided along the meshes of the second rotating disc are oriented to openings surrounded by the thin elements which form the meshes in the first rotating disc. Then, the projections of the adjacent rotating discs mutually protrude toward the openings in the respective meshes. As a result, the rotating biological contactor-type sewage treatment equipment of the present invention shows the following functions (i)-(v), which enhance efficiency in sewage treatment.
(i) Between adjacent rotating discs, the thin elements which form the meshes cooperate with the projections to construct a three-dimensional structure. These thin elements and projections always maintain a predetermined space in all of the three-dimensional directions, so that they do not contact each other. Therefore, the rotating discs make a sufficient contact with air and sewage, without the fear of clogging.
(ii) The rotating discs have a large surface area per unit volume.
(iii) The sewage treatment equipment does not block water flow in the axial direction, thereby providing many practical treatment stages.
(iv) The aeration effect due to the projections on the discs increases the amount of oxygen supply to sewage.
(v) The sewage treatment equipment is rich in biofilms which induce a transfer phenomenon on a macro scale.
Further, with the following functions (1)-(3), the rotating biological contactor-type sewage treatment equipment of the present invention improves safety in sewage treatment.
(1) Biofilms on all rotating discs do not slough off at a time, which prevents deterioration of treated water.
(2) Since biofilms are spaced evenly, the meshes are not clogged by excessive attachment of the biofilms.
(3) The rotating discs receive stresses caused by various factors (e.g. resistance of sewage, attachment condition of aerobic bacteria). Nevertheless, the rotating discs can maintain the mechanical strength against such stresses.
Incidentally, the rotating discs used in the present invention can be made of conventional materials for rotating discs, without particular limitations. For example, use can be made of vinyl chloride resins, polyethylenes, polypropylenes, polycarbonates, FRPs and other synthetic resins, as well as stainless steel, aluminium and other metals.